High switching rate (&gt;200 MHz) light emitting diode sources appear quite promising for many fiber-optic communication applications. Light emitting diodes operating in the spontaneous mode (LED's) instead of the stimulated mode (laser diodes) can perform quite satisfactorily even though decreased output powers and decreased speeds are inherent. LED's are cheaper to make and have much longer operating lives than laser diodes.
It is well known that the lifetime of injected carriers in an LED decreases as the doping concentration of the active region increases and that decreased lifetime of injected carriers allows the LED to respond more quickly to switching signals thereby permitting high speed operation. Accordingly, prior art LED's have heavily doped (.apprxeq.10.sup.19 /cm.sup.3) active regions. Unfortunately, the internal quantum efficiency of LED's also decreases with increased doping concentration. For example, as doping concentration increases the width of the depletion region decreases, resulting in carrier tunneling across the depletion region. The tunneling makes use of local band gap states due to imperfections and hence is a non-radiation producing recombination.